Artificial multilayer and method of manufacturing the same

ABSTRACT

Disclosed is an artificial multilayer in which ferromagnetic layers and nonmagnetic layers are alternatively laminated, wherein a uniaxial magnetic anisotropy is introduced into the ferromagnetic layers in a predetermined direction, thereby controlling the gradient of the relative change of resistivity to the change of external magnetic field. The uniaxial magnetic anisotropy is introduced into the ferromagnetic layers by applying a magnetic field along the surface of ferromagnetic layers during the formation thereof.

This is a continuation of application Ser. No. 08/424,082 filed on Apr.19, 1995, now U.S. Pat. No. 5,534,355 which is a continuation of Ser.No. 08/120,236 filed on Sep. 14, 1993, now abandoned which is acontinuation of Ser. No. 07/786,727 filed on Nov. 1, 1991 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an artificial multilayer having amagnetoresistance effect and a method of manufacturing the same.

2. Description of the Related Art

Am electrical resistivity ρ of a substance, which has a specific valueat a predetermined temperature, varies with application of an externalmagnetic field. This phenomenon is called "a magnetoresistance effect",which is one of galvanomagnetic effects in the same manner as a Halleffect.

This magnetoresistance effect is applied to magnetoresistive elementssuch as a magnetoresistive field sensor, or a magnetoresistive head (MRhead). As a material exhibiting the magnetoresistance effect, asemiconductor and a ferromagnetic material are known.

Since the physical properties of the semiconductor generally varylargely depending on temperature, the upper limit of its operatingtemperature is restricted to about 100° C. On the contrary, theferromagnetic material has a small temperature coefficient, and theupper limit of its operating temperature is a Curie point in principle,so that the ferromagnetic material can be used up to much highertemperature as compared with the semiconductor. Further, since theferromagnetic material can easily be formed in a thin film andminiaturized, a magnetoresistive element made of the ferromagneticmaterial can effectively detect a magnetic field even if a distancebetween magnetic charges is as short as μm order.

The magnetoresistance effect of the ferromagnetic material observed whenan external magnetic field is relatively weak has a feature that itsresistivity varies according to an angle formed between a magnetizingdirection and a current direction. This phenomenon is particularlycalled an anisotropic magnetoresistance effect. The resistivity ofgeneral ferromagnetic metal takes maximum when its magnetizing directionis parallel to a current direction (ρ) and minimum when both are crossedperpendicularly to each other (ρ⊥). As a quantity of representing themagnitude of the anisotropic magnetoresistance effect, a ratio Δρ/ρ₀ isused, where Δρ=ρ-ρ⊥, and ρ₀ is the resistivity when an applied magneticfield is zero. As materials having large Δπ/π₀ at a room temperature,Ni-Co or Ni-Fe based alloys are known. Noted that their Δρ/ρ₀ are nomore than about 2.5 to 6.5%.

It has been recently reported that a large magnetoresistance effect isobserved in an artificial multilayer in which ferromagnetic layers andnonmagnetic layers are alternatively laminated and magnetization ofadjacent ferromagnetic layers are arranged in antiparallel (Phys. Rev.Lett. Vol. 61. p. 2472 (1988)). For example, a multilayer consisting ofFe (a ferromagnetic layer)/Cr (a nonmagnetic layer) system is known. TheFe/Cr multilayer formed on a glass substrate, the maximum relativechange of resistivity (ρ_(s) -ρ₀)/ρ₀, where ρ₀ is the resistivity whenan applied magnetic field is zero and ρ_(s) is the resistivity when themagnetization is saturated, has very large values of -8.4% at a roomtemperature and -26.4% at 77K (J. App. Mag. Soc. vol. 14, p. 351(1990)). In such a type of artificial multilayer, however, a saturatedmagnetic field, i.e. an external magnetic field required to saturate therelative change of resistivity, is 10 kOe or more at a room temperaturewhich much exceeds a practical range required for a magnetoresistivefield sensor or an MR head.

Further, it is reported that artificial multilayers other than Fe/Crsystem, for example Ni-Fe/Cu/Co/Cu system (J. Phys. Soc. Jap. 59 (1990)3016) or Ni-Fe/Cu/Ni-Fe/FeMn system (35th Annual Conference on Magnetismand Magnetic Materials, 1990), also exhibit a large magnetoresistanceeffect.

In these artificial multilayers, an antiparallel aligned state ofmagnetization which leads to the large magnetoresistance effect, isrealized on the way of magnetizing process due to a difference ofanisotropies of two types of ferromagnetic layers, that is, a hard layer(a layer having a large magnetic anisotropy) such as Co or FeMn/Ni-Fe,and a soft layer (a layer having a small magnetic anisotropy) such asNi-Fe (permalloy). The Ni-Fe/Cu/Co/Cu system, however, exhibits a largehysteresis in the magnetoresistance effect with respect to the magneticfield. Therefore, it is required to reduce the hysteresis as small aspossible. On the other hand, the Ni-Fe/Cu/Ni-Fe/FeMn system exhibits asmall hysteresis in a weak magnetic field up to 15 Oe. Further, itsrelative change of resistivity Δρ/ρ₀ varies stepwise to the change ofexternal magnetic field ΔH, that is preferable in practical use. In viewof various applications of the magnetoresistance effect, however, it ismore preferable to be able to control the relative change of resistivityso as to vary at an arbitrary gradient to the change of externalmagnetic field, rather than stepwise variation.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anartificial multilayer of which relative change of resistivity Δρ/ρ₀ canbe controlled so as to vary at an arbitrary gradient to the change ofmagnetic field ΔH.

An artificial multilayer according to the present invention comprisesferromagnetic layers and nonmagnetic layers which are alternativelylaminated, wherein a uniaxial magnetic anisotropy is introduced into theferromagnetic layers in a predetermined direction along the surface ofthe multilayer.

A method of manufacturing the artificial multilayer according to thepresent invention comprises a step of introducing a uniaxial magneticanisotropy into the ferromagnetic layers in a predetermined direction byapplying a magnetic field along the surface of the ferromagnetic layers.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1A is a view showing the construction of an ion beam sputteringapparatus used in an embodiment of the present invention, FIGS. 1B and1C are plan views showing dispositions of means for applying magneticfield at the periphery of a substrate;

FIG. 2 is a sectional view showing the arrangement of an artificialmultilayer of Example 1;

FIG. 3A shows the magnetization curve of the artificial multilayer ofComparative Example 1, and FIG. 3B shows a magnetization curve of theartificial multilayer of the Example 1;

FIG. 4A shows the magnetoresistance effect of the artificial multilayerof Comparative Example 1, and FIG. 4B shows the magnetoresistance effectof the artificial multilayer of the Example 1;

FIG. 5 is a sectional view showing the arrangement of an artificialmultilayer of Example 6;

FIG. 6 is a sectional view showing the magnetoresistance effect of theartificial multilayer of Example 6;

FIG. 7 is a sectional view showing the arrangement of an artificialmultilayer of Example 7;

FIG. 8A is a diagram showing the case that the directions of uniaxialmagnetic anisotropies introduced into a soft layer and a hard layer areparallel, and FIG. 8B is a diagram showing the case that the directionsof uniaxial magnetic anisotropies introduced to the soft layer and thehard layer are crossed perpendicularly, with regard to the artificialmultilayer of Example 7;

FIG. 9A shows the magnetoresistance effect of the artificial multilayerof Example 7 shown in FIG. 8A, and FIG. 9B shows the magnetoresistanceeffect of the artificial multilayer of Example 7 shown in FIG. 8B;

FIG. 10 is a sectional view showing the arrangement of the artificialmultilayer of Example 8;

FIG. 11 is a view showing the construction of an RF magnetron sputteringapparatus used in Example 9;

FIG. 12A is the X-ray diffraction chart of the artificial multilayer ofSample A, and FIG. 12B is the X-ray diffraction chart of the artificialmultilayer of Sample B, in Example 9; and

FIG. 13A shows the magnetoresistance effect when the direction of themagnetic field is crossed perpendicularly to that of the current, andFIG. 13B shows the magnetoresistance effect when the direction of themagnetic field is parallel to that of the current, with regard to thesample A of the example 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, a ferromagnetic layer consists of at least oneselected from a group of transition metals such as Fe, Co, Ni, and theiralloys and compounds. The word "nonmagnetic" includes paramagnetic andantiferromagnetic. A nonmagnetic layer consists of at least one selectedfrom a group of transition metals such as V, Cr, Cu, Au, etc., and theiralloys and compounds. These layers may be crystalline or amorphous. Thethickness of the ferromagnetic layer is preferably 0.5 to 20 nm, thethickness of the nonmagnetic layer is preferably 0.5 to 20 nm, and thethickness of the entire laminated layers is preferably 30 to 500 nm.

In the present invention, the artificial multilayer includes amultilayer in which different types of layers are coherently laminatedor different types of layers, though not coherently, but are laminatedunder the control of the thickness in an accuracy of several angstrom to10 nm.

In the present invention, a uniaxial magnetic anisotropy is introducedto the ferromagnetic layers constitute the artificial multilayer in apredetermined direction along the surface of the multilayer. Forexample, the uniaxial magnetic anisotropy can be introduced by applyinga magnetic field of 20 to 500 Oe along the surface of the multilayer atthe time of formation of multilayer by sputtering, etc. The uniaxialmagnetic anisotropy can also be introduced by heat treating themultilayer in the magnetic field after the multilayer is formed.

The artificial multilayer of the present invention may be formed on anarbitrary substrate, that is, a non-singlecrystalline substrate made ofsuch as glass, or a singlecrystalline substrate made of such as Si.

The uniaxial magnetic anisotropy can also be introduced in theferromagnetic layers by forming epitaxial-growth-multilayer which hassingle crystal structure in each layer. By selecting a suitable singlecrystal substrate, crystal orientation of single crystal ferromagneticlayers can be controlled, and as a result, it is possible to change thedirection of crystalline magnetic anisotropy which originates fromcrystalline symmetry.

In the artificial multilayer according to the present invention, theelectrical resistivity of the ferromagnetic layers takes maximum whenmagnetizations of adjacent two ferromagnetic layers are alignedantiparallel to each other and minimum when aligned in parallel witheach other. In the case of Fe/Cr multilayer, the antiparallel alignedstate of magnetizations of the ferromagnetic layers is obtained by anantiparallel coupling itself of the ferromagnetic layers through theantiferromagnetic layer (Cr). In the artificial multilayer utilizing adifference between magnetic anisotropies of two types of ferromagneticlayers, i.e. a hard layer and a soft layer, the antiparallel alignedstate of magnetizations of the ferromagnetic layers occurs on the way ofa magnetizing process. The antiparallel aligned state is converted to aparallel aligned state by an external magnetic field. As a result, theresistivity of the ferromagnetic layers is varied.

In the artificial multilayer formed on a non-singlecrystalline substratesuch as a glass substrate in a nonmagnetic field as in prior art, theferromagnetic layers have an easy axis of magnetization along theirsurfaces due to a demagnetizing field, but its direction is isotropic inthe plane, so that the easy axis exists in various directions.

On the contrary, when a uniaxial magnetic anisotropy is introduced tothe artificial multilayer utilizing an antiferromagnetic couplingbetween the ferromagnetic layers such as Fe/Cr system, the easy axis ofmagnetization of the ferromagnetic layers directs to one direction inthe surface of the layers. Therefore, when the resistivity of such aartificial multilayer is measured with applying an external magneticfield in that direction, a saturated magnetic field is reduced ascompared with those which is formed in nonmagnetic field and of whicheasy axis is isotropic in the plane. When its resistivity is measuredwith the uniaxial magnetic anisotropy being directed at a certain angleθ with respect to the direction of the external magnetic field, thegradient of the relative change of resistivity Δρ/ρ₀ to the change ofmagnetic field ΔH, i.e. (Δρ/ρ₀)/ΔH, will be gentle, although thesaturated magnetic field is increased. Such a gentle gradient isconvenient to detect the magnitude of the external magnetic field.

In the case of the artificial multilayer utilizing both of a soft layerand a hard layer, there are two combinations due to ways of introducinga uniaxial magnetic anisotropy to both layers.

In one method, uniaxial magnetic anisotropies are introduced in the samedirections to both of the soft and hard layers. In this case, similarlyto the above, when its resistivity is measured with applying an externalmagnetic field in the direction of the uniaxial magnetic anisotropy, asaturated magnetic field is reduced, and its hysteresis can be reduced.When its resistivity is measured with the uniaxial magnetic anisotropybeing directed at a certain angle θ with respect to the direction of theexternal magnetic field, the gradient (Δρ/ρ₀)/ΔH will be gentle,resulting to be convenient to detect the magnitude of the externalmagnetic field.

In the other method, uniaxial magnetic anisotropies are introduced inthe different directions to the soft and hard layers. It is preferableto set an angle formed between the directions of uniaxial magneticanisotropies to be introduced into the both layers to 30°<θ<90°. In thiscase, when its resistivity is measured with the uniaxial magneticanisotropy of the soft layer, in particular, being directed at a certainangle θ with respect to the direction of the external magnetic field,the gradient (Δρ/ρ₀)/ΔH can be controlled. When it is measured bysetting θ=0°, a stepwise change of magnetoresistance can be obtained.

In any of the above-described cases, the gradient (Δρ/ρ₀)/ΔH will becomemost abrupt when the angle θ=0° formed between the direction of theintroduced uniaxial magnetic anisotropy and the direction of theexternal magnetic field, and most gentle when the angle θ=90°. In orderto obtain a gradient convenient to detect the magnitude of the externalmagnetic field, it is preferable to set to 30°<θ<90°.

EXAMPLES

Examples of the present invention will be described.

Example 1

FIG. 1A shows an ion beam sputtering apparatus used in this example. Anexhaust port 2 of a chamber 1 is connected to a vacuum pump (not shown),and the pressure in the chamber 1 is measured by a pressure gauge 3. Asubstrate holder 4 is installed in the chamber 1, and a substrate 5 isheld on the substrate holder 4. A heater 6 is provided in the substrateholder 4, and cooling water 7 is flowed near the substrate holder 4 toregulate the temperatures of the substrate holder 4 and the substrate 5.The temperature of the substrate holder 4 is measured with athermocouple 8. Means for applying magnetic field 9 is provided near thesubstrate 5 to apply a magnetic field along the surface of a layer to beformed on the substrate 5. A shutter 10 is provided in front of thesubstrate 5. A target holder 11 is rotatably provided at a positionopposed to the substrate 5, and a plurality of targets 12 are mounted onthe surface of target holder 11. The target holder 11 is cooled bycooling water 13. An ion gun 14 is provided at a position opposed to thetargets 12, and Ar gas 15 is supplied to the ion gun 14.

As the means for applying magnetic field 9, as shown in FIG. 1B, a pairof permanent magnets 16 may be provided, or, as shown in FIG. 1C, twopairs of Helmholtz coils 17a and 17b may be provided. In the case ofFIG. 1C, the direction of the magnetic field can be altered indirections perpendicular to each other according to which of the twopairs of Helmholtz coils 17a and 17b are used.

An artificial multilayer having layers of Fe/Cr was manufactured byusing an ion beam sputtering apparatus shown in FIG. 1A. As thesubstrate 5, quartz glass was employed. Two types of targets 12 made ofFe and Cr were mounted on the target holder 11. The chamber 1 wasexhausted up to 2×10⁻⁷ Torr, and then Ar gas was introduced into the iongun 14 to set the pressure to 3×10⁻⁴ Torr. Ar was ionized andaccelerated, and then emitted to the target 12 with the energy of 500eV. The temperature of the substrate was varied from a room temperatureto 400° C. Two types of targets were rotated at each predetermined timeto alternatively laminate Fe layer 102 and Cr layer 103 on the quartzglass substrate 21, as shown in FIG. 2, thereby manufacturing anartificial multilayer. During this process, a magnetic field of 100 Oewas applied to the layers by a pair of permanent magnets 16 shown inFIG. 1B to introduce a uniaxial magnetic anisotropy in a predetermineddirection in the surface of the layers (Example 1).

In comparison, an artificial multilayer was manufactured similarly tothe above process except that the layers are formed in a nonmagneticfield without using permanent magnets (Comparative example 1).

The artificial multilayers obtained as described 10 above are expressedby (t_(Fe) /t_(Cr))_(n), where t_(Fe) (nm) is the thickness of the Felayer, t_(Cr) (nm) is the thickness of the Cr layer, and n is the numberof repetition of a pair of the Fe layer and the Cr layer. In thisexample, the artificial multilayer of (t_(Fe) /t_(Cr))_(n) =(2.7/1.3)₇was manufactured.

FIGS. 3A and 3B respectively show magnetization curves of the artificialmultilayers of the comparative example 1 and the example 1. From FIGS.3A and 3B, it is understood that the saturated magnetic field is 2.5 kOeor more in the artificial multilayer of Comparative Example 1manufactured in the nonmagnetic field, whereas it is 1.6 kOe in theartificial multilayer of Example 1 manufactured in the magnetic field.Thus, since the uniaxial magnetic anisotropy is introduced in onedirection in the surface of the multilayer of Example 1, its saturatedmagnetic field is reduced.

FIGS. 4A and 4B respectively show the magnetoresistance effects of theartificial multilayers of Comparative Example 1 and Example 1. At thetime of measurements, the direction of a current was set parallel tothat of the external magnetic field. The artificial multilayer ofExample 1 formed in a magnetic field was measured in such a manner thatthe direction of the uniaxial magnetic anisotropy was set to that of theexternal magnetic field. As understood from FIGS. 4A and 4B, theexternal magnetic field for saturating the relative change ofresistivity is about 3 kOe in the artificial multilayer of ComparativeExample 1, and 2 kOe or less in the artificial multilayer of Example 1.Similarly to the results of FIGS. 3A and 3B, since the uniaxial magneticanisotropy is introduced into one direction in the surface of themultilayer in Example 1, its saturated magnetic field is reduced.

Even when measurements were executed by crossing the direction of thecurrent perpendicularly to that of the magnetic field, similar resultsto those of FIGS. 4A and 4B were obtained.

Example 2

Similarly to the example 1, amorphous alloys shown in Table 1 having athickness of 3 nm as ferromagnetic layers and Cu having a thickness of 1nm as nonmagnetic layers were alternatively laminated on a quartz glasssubstrate, and an artificial multilayer having an entire thickness of 50nm was manufactured.

The results of the resistivity and relative change of resistivity of theartificial multilayers measured by a four-point method at a roomtemperature are shown in Table 1.

As shown in Table 1, for example, the resistivity of the artificialmultilayer utilizing the amorphous alloy of Sample No. 5 is 130 μΩ-cm.This value is slightly larger than that of the amorphous alloy only. Itsrelative change of resistivity was saturated in the low magnetic field(several hundreds Oe), and the relative change of this case was about-10%. This relative change is calculated in terms of variation in theresistivity of 13 μΩ-cm. Therefore, when the multilayer is applied as amagnetoresistive element, a large output is obtained upon the change ofthe resistivity. This is advantageous in practical use of themagnetoresistive element.

                  TABLE 1                                                         ______________________________________                                        Sample Composition of                                                                              Resistivity                                                                              Relative change                               Nos.   alloys (at %) (μΩ-cm)                                                                         of resistivity                                ______________________________________                                        1      Fe.sub.75 Si.sub.12.5 B.sub.12.5                                                            162        -8.5                                          2      Fe.sub.73 B.sub.27                                                                          158        -7.2                                          3      (Co.sub.0.94 Fe.sub.0.06).sub.70 B.sub.30                                                   164        -7.0                                          4      Co.sub.85 Zr.sub.15                                                                         147        -9.3                                          5      Co.sub.80 Zr.sub.10 Nb.sub.10                                                               130        -9.8                                          ______________________________________                                    

Example 3

Similarly to the example 1, the amorphous alloy of Sample No. 4 in Table1 having a thickness of 3 nm as ferromagnetic layers and Cr having athickness of 1 nm as nonmagnetic layers instead of the Cu of Example 2were alternatively laminated on a quartz glass substrate, and anartificial multilayer having an entire thickness of 50 nm wasmanufactured.

From the measurements of the artificial multilayer by a four-pointmethod at a room temperature, its resistivity was 160 μΩ-cm, and therelative change of resistivity was -7% at the saturated magnetic fieldof 300 Oe.

Example 4

Similarly to the example 1, Fe-based alloys shown in Table 2 having athickness of 2 nm as ferromagnetic layers and Cr having a thickness of1.2 nm as nonmagnetic layers were alternatively laminated on a quartzglass substrate, and an artificial multilayer having an entire thicknessof 64 nm was manufactured.

The values of saturated magnetic field of the artificial multilayerswere measured when an external magnetic field was applied in thedirection of easy axis (θ=0°) and the direction of difficult axis(θ=90°). In comparison, the saturated magnetic field of the artificialmultilayers formed in nonmagnetic field were also measured. Thesemeasurement results are shown in Table 2.

As understood from Table 2, when the external magnetic field is appliedin the direction of the easy axis (in the direction of uniaxial magneticanisotropy) of the artificial multilayer according to the presentinvention, the saturated magnetic field can be reduced as compared withthe artificial multilayer formed in nonmagnetic field and in whichuniaxial magnetic anisotropy is not introduced. When the externalmagnetic field is applied in the direction of difficult axis (in adirection perpendicular to the uniaxial magnetic anisotropy) of theartificial multilayer according to the present invention, the saturatedmagnetic field is increased. From these results, it is understood thatthe magnitude of the saturated magnetic field can be controlled byvarying θ between 0° and 90°.

                  TABLE 2                                                         ______________________________________                                                    Saturated magnetic field (KOe)                                                Multilayer formed                                                             in magnetic field                                                 Sample                                                                              Composition of                                                                            easy   difficult                                                                             Multilayer formed                            Nos.  alloys (at %)                                                                             axis   axis    in nonmagnetic field                         ______________________________________                                        11    Fe.sub.95 Co.sub.5                                                                        3.3    4.2     3.5                                          12    Fe.sub.90 Co.sub.10                                                                       3.1    4.6     3.8                                          13    Fe.sub.80 Co.sub.20                                                                       1.6    2.9     2.2                                          14    Fe.sub.75 Co.sub.25                                                                       0.9    2.1     1.5                                          ______________________________________                                    

Example 5

An Fe/Cr artificial multilayer of (t_(Fe) /t_(Cr))_(n) =(2.5/1.3)₃₀ wasmanufactured on a quartz glass substrate (at room temperature) by thesimilar method to that of Example 1 except that the magnetic field isnot applied. The saturated magnetic field of the artificial multilayerwas 2.7 kOe.

Then, the artificial multilayer was heat treated at 50° C. in vacuum ina magnetic field. With regard to the obtained artificial multilayer, thesaturated magnetic field was reduced to 2.2 kOe when the externalmagnetic field was applied in the direction of easy axis, while wasincreased to 3.2 kOe when the external magnetic field was applied in thedirection of difficult axis.

Example 6

An artificial multilayer shown in FIG. 5 was manufactured by using anion beam sputtering apparatus of FIG. 1A. As a substrate, quartz glasswas used, and as targets, Co, Cu, Ni and Fe were used. A pair ofpermanent magnets 16 were disposed oppositely near a substrate holder asshown in FIG. 1B, and a multilayer was formed in a magnetic field of 100Oe.

This artificial multilayer has a structure in which N layers oflaminated layers each having a Co layer 22 having a thickness of 2.5 nm,a Cu layer 23 having a thickness of 5 nm, an (Ni/Fe)_(n) layer 26 inwhich Ni layers 24 having a thickness of 2 nm and Fe layers 25 having athickness of 2 nm are alternately laminated, and a Cu layer 23 having athickness of 5 nm to be sequentially laminated, are repeatedly formed.

The artificial multilayer is represented by [(Ni/Fe)_(n) /Cu/Co/Cu]_(N).In this artificial multilayer, the (Ni/Fe)_(n) layer is a soft layer,the Cu layer is a nonmagnetic layer, and the Co layer is a hard layer.

The result in which the magnetoresistance effect of the artificialmultilayer is measured in a minor loop of ±10 Oe in which the directionof the uniaxial magnetic anisotropy is parallel to that of the externalmagnetic field is shown in FIG. 6. It is understood from FIG. 6 that aslight hysteresis is observed, but the relative change of resistivity isvaried stepwise to the magnetic field.

Example 7

An artificial multilayer shown in FIG. 7 was manufactured by using anion beam sputtering apparatus of FIG. 1A. As a substrate, quartz glasswas used, and as targets, permalloy (Ni₈₀ Fe₂₀), Cu, Co, Gd-Co compound,and Ag were used. A substrate temperature was set to 150° to 400° C.during the layer formation. Two pairs of Helmholtz coils 17a, 17b shownin FIG. 1C were disposed near a substrate holder, and the multilayer wasformed in a magnetic field of 100 Oe.

This artificial multilayer has a structure in which a permalloy (Ni₈₀Fe₂₀) layer 32, a Cu layer 33, a Co layer 24, a Gd-Co layer 35 and an Aglayer 36 are sequentially laminated on a quartz glass substrate 21.

This artificial multilayer is represented as permalloy/Cu/(Co/Gd-Co)/Ag.In the artificial multilayer, the permalloy layer is a soft layer, theCu layer is a nonmagnetic layer, the Co layer is a hard layer, the Gd-Colayer has an effect for imparting exchange anisotropy to the Co layer,and the Ag layer is a protective layer.

The uniaxial magnetic anisotropy was introduced in two combinationsshown in FIGS. 8A and 8B by selecting the use of any of the Helmholtzcoils 17a and 17b. In FIG. 8, the direction of the uniaxial magneticanisotropy is denoted by arrows with a solid line. That is, in FIG. 8A,the direction of the uniaxial magnetic anisotropy introduced to the softlayer is parallel to that of the uniaxial magnetic anisotropy introducedto the hard layer. On the other hand, in FIG. 8B, the direction of theuniaxial magnetic anisotropy introduced to the soft layer is crossedperpendicularly to that of the uniaxial magnetic anisotropy introducedto the hard layer.

The magnetoresistance effects of the artificial multilayers obtained asdescribed above were measured in a minor loop of ±20 Oe. At the time ofthe measurements, the direction of the uniaxial magnetic anisotropyintroduced to the hard layer was parallel to that of the externalmagnetic field (denoted by an arrow with a broken line in FIG. 8).Therefore, the angle formed between the direction of the uniaxialmagnetic anisotropy of the soft layer and the direction of the externalmagnetic field is 0° or 90°. These results are respectively shown inFIGS. 9A and 9B.

As apparent from FIGS. 9A and 9B, the gradient of the relative change ofresistivity to the change of magnetic field, i.e. (Δρ/ρ₀)/ΔH, is mostabrupt to exhibit a stepwise change in the case of θ=0°, and most gentlein the case of θ=90°. From these results, it is understood that thegradient (Δρ/ρ₀)/ΔH can be controlled by setting the direction of theuniaxial magnetic anisotropy of the soft layer to an arbitrary angle θto the direction of the external magnetic field.

Example 8

An artificial multilayer shown in FIG. 10 was manufactured by using anion beam sputtering apparatus of FIG. 1A. As a substrate, quartz glasswas used, and as targets, Ni, Fe, Cu, Co, Gd-Co compound, and Ag wereused. Two pairs of Helmholtz coils 17a and 17b shown in FIG. 1C weredisposed near the substrate holder, and a multilayer was formed in amagnetic field of 100 Oe.

This artificial multilayer has a structure in which an (Ni/Fe)_(n) layer44 in which Ni layers 42 and Fe layers 43 are alternatively laminated, aCu layer 45, a Co layer 46, a Gd-Co layer 47 and an Ag layer 48 aresequentially laminated on a quartz glass substrate 21.

This artificial multilayer is expressed as (Ni/Fe)_(n)/Cu/(Co/Gd-Co)/Ag. In this artificial multilayer, the (Ni/Fe)_(n) layeris a soft layer, the Cu layer is a nonmagnetic layer, the Co layer is ahard layer, the Gd-Co layer has an effect for imparting exchangeanisotropy to the Co layer, and the Ag layer is a protective film.

Similarly to Example 7, the uniaxial magnetic anisotropy was introducedin two combinations as shown in FIGS. 8A and 8B to the soft and hardlayers by selecting the use of any of the Helmholtz coils 17a and 17b,and an artificial multilayer was manufactured.

The magnetoresistance effects of the artificial multilayers weremeasured in a minor loop of ±20 Oe. At the time of the measurements, thedirection of the external magnetic field was brought into coincidencewith that of the uniaxial magnetic anisotropy introduced to the hardlayer. Even in this case, the similar results to those of Example 7 (inFIGS. 9A and 9B) were obtained, and a hysteresis was slightly reduced ascompared with that of Example 7.

Example 9

In the examples described above, the artificial multilayers weremanufactured by using the ion beam sputtering apparatus. However, theartificial multilayer may also be manufactured by using other apparatussuch as an RF magnetron sputtering apparatus.

FIG. 11 shows an RF magnetron sputtering apparatus used in this example.An atmosphere in a chamber 51 is exhausted from an exhaust port 52, andAr gas is introduced from a gas inlet 53 into the chamber 51. Asubstrate 54 is held at the top of the chamber 51. Targets 55 are heldoppositely to the substrate 54 in the lower section of the chamber 51,and shutters 56 are provided at the targets 55 of the sides of thesubstrate 54. An electric field is applied from an RF power supply 57 tothe targets 55 through a matching box 58. A magnetic field is applied toa space between the targets 55 and the substrate 54 by magnets 59.

An artificial multilayer having layers of Fe/Cr was manufactured byusing the RF magnetron sputtering apparatus of FIG. 11. As the substrate54, MgO was used, and as the targets 56, Fe and Cr were used. Thechamber was exhausted up to 5×10⁻⁶ Torr. The conditions of forming thelayers of Fe and Cr were set to the two types of conditions shown inTable 3. The shutters 57 of the targets 56 were alternatively opened andclosed to form the multilayer, and two types of artificial multilayersof Samples A and B represented by (t_(Fe) /t_(Cr))_(n) =(2.7/1.3)₁₀ weremanufactured.

                  TABLE 3                                                         ______________________________________                                                           Sample A  Sample B                                         Ar pressure (Torr) 8 × 10.sup.-3                                                                     5 × 10.sup.-3                              ______________________________________                                        FE       RF power (W)  300       600                                                   Forming rate  0.021     0.045                                                 (nm/sec.)                                                            Cr       RF Power (W)  150       300                                                   Forming rate  0.062     0.13                                                  (nm/sec.)                                                            ______________________________________                                    

An X-ray diffraction patterns of the artificial multilayers manufacturedas described above are shown in FIGS. 12A and 12B. With regard to SampleA, tertiary peaks are observed which reflects the periodicity of theartificial multilayer. On the other hand, with regard to Sample B, onlysecondary peaks are observed. From these results, it is understood thatthe boundary between the Fe layer and the Cr layer is relatively sharpin Sample A, in other word, mixing of Fe atoms and Cr atoms was slightin the boundary. On the other hand, since the tertiary peaks are notobserved in Sample B, it is understood that mixing of Fe and Cr atomsoccurred in the boundary of the Fe layer and Cr layer.

FIGS. 13A and 13B show the magnetoresistance effects of the artificialmultilayer of Sample A when the direction of the magnetic field wascrossed perpendicularly to that of the current and the directions ofboth were parallel. As apparent from FIGS. 13A and 13B, the relativechange of resistivity when the direction of the magnetic field wascrossed perpendicularly to that of the current (FIG. 13A), is largerthan that when the directions of the magnetic field and the current wereparallel (FIG. 13B). In FIG. 13A, when the magnetic field of 3 kOe wasapplied, 10% of relative change of resistivity was observed.

In the case of Sample B, though not shown, the symbols of relativechange of resistivity were different (plus or minus) according to thedirections of the magnetic field and the current being eitherperpendicular or parallel. The magnitude of the relative change ofresistivity was very small to 0.5% or less. These results exhibit asimilar magnetoresistance effect generally observed in the ferromagneticmaterial such as Ni, in which the effect as the artificial multilayer isnot present.

From the above-described results, it is understood that, since the metalatoms reaching the substrate have excessively high energy under thegeneral layer forming conditions according to the RF magnettonsputtering apparatus (for example, Ar pressure: 3-5×10⁻³ Torr, formingrate: 0.1 nm/sec. or more), atoms on the substrate are feasibly mobile,and mixing of the atoms in the laminated layers occurs, therefore theartificial multilayer having a sharp boundary is not obtained.

On the contrary, when the RF power is lowered in a range capable ofsputtering as the condition for Sample A, the artificial multilayerhaving a sharp boundary is readily obtained. More specifically, it ispreferable to set the RF power for the formation of the layers to 400 Wor less in the case of Fe and 200 W or less in the case of Cr. However,when the RF power is extremely reduced, stable forming rate cannot beobtained. Therefore, it is preferable to set the RF power to 200 W ormore for Fe layers and to 50 W or more for Cr layers. It is alsoeffective to reduce the energy of the metal atoms reaching the substrateby setting the Ar pressure to 7×10⁻⁷ Torr or more by the same reasondescribed above.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method of manufacturing a multilayerconstituting a magnetoresistance device comprising the stepsof:depositing ferromagnetic and nonmagnetic layers alternately on asubstrate having a non-singlecrystalline surface, each of saidferromagnetic layers having a thickness between 0.5 nm and 20 nm; andintroducing a uniaxial magnetic anisotropy into said ferromagneticlayers by applying a magnetic field that is parallel to the majorsurface of said ferromagnetic layers during the formation thereof or byannealing in a magnetic field that is parallel to the major surface ofsaid ferromagnetic layers after the formation thereof, thus forming amultilayer structure; and coupling a means to said multilayer structurefor measuring resistivity of the multilayer structure along a directionwhich is parallel to the layers of the multilayer structure.
 2. Themethod according to claim 1, wherein said ferromagnetic layers consistof at least one selected from a group consisting of Fe, Co, Ni, andtheir alloys and compounds, and said nonmagnetic layers consist of atleast one selected from a group consisting of V, Cr, Cu, An, and theiralloys and compounds.
 3. The method according to claim 1, wherein saidferromagnetic layers consist of a single material.
 4. The methodaccording to claim 1, wherein said ferromagnetic layers consist ofdifferent materials.
 5. The method according to claim 4, wherein saidmaterials forming the ferromagnetic layers differ from each other in themagnitude of the magnetic anisotropy.
 6. The method according to claim4, wherein the direction of the uniaxial magnetic anisotropy in a firstferromagnetic layer differs from that in a second ferromagnetic layeradjacent to said first ferromagnetic layer.
 7. The method according toclaim 6, wherein the directions of the uniaxial magnetic anisotropies ofthe two adjacent ferromagnetic layers form an angle of 30° to 90°. 8.The method according to claim 1, wherein the thickness of each of saidnonmagnetic layers ranges between 0.5 to 20 nm, and the entire thicknessof laminated layers ranges between 30 to 500 nm.
 9. The method accordingto claim 1, wherein said substrate is a glass substrate.